Ma. Bittinger et al., ROSR, A DETERMINANT OF NODULATION COMPETITIVENESS IN RHIZOBIUM-ETLI, Molecular plant-microbe interactions, 10(2), 1997, pp. 180-186
We previously described a Tn5 mutant of Rhizobium etli strain CE3, des
ignated CE3003, that is decreased in nodulation competitiveness, reduc
ed in competitive growth in the rhizosphere, and has a hydrophobic cel
l surface (R. S. Araujo, E. A. Robleto, and J. Handelsman, Appl. Envir
on, Microbiol., 60:1430-1436, 1994), To determine the molecular basis
for the mutant phenotypes, we identified a 1.2-kb fragment of DNA deri
ved from the parent that restored the wild-type phenotypes to the muta
nt. DNA sequence analysis indicated that this 1.2-kb fragment containe
d a single open reading frame that we designated rosR. The Tn5 inserti
on in CE3003 was within rosR. We constructed a derivative of CE3 that
contained a deletion in rosR, and this mutant was phenotypically indis
tinguishable from CE3003 in cell surface and competitive characteristi
cs. Based on the nucleotide sequence, the deduced RosR amino acid sequ
ence is 80% identical to that of the Ros protein from Agrobacterium tu
mefaciens and the MucR protein from Rhizobium meliloti. Both Ros and M
ucR are transcriptional repressors that contain a putative zinc-finger
DNA-binding domain, This study defines a gene, rosR, that is homologo
us to a family of transcriptional regulators and contributes to nodula
tion competitiveness of R. etli. Moreover, we established that a singl
e gene affects nodulation competitiveness, competitive growth in the r
hizosphere, and cell surface hydrophobicity.